Which spectral class does the sun belong to

But we saw above that hydrogen lines alone are not a good indicator for classifying stars, since their lines disappear from the visible light spectrum when the stars get too hot or too cold. Instead of starting over, Cannon also rearranged the existing classes—in order of decreasing temperature—into the sequence we have learned: O, B, A, F, G, K, M.

As you can read in the feature on Annie Cannon: Classifier of the Stars in this chapter, she classified around , stars over her lifetime, classifying up to three stars per minute by looking at the stellar spectra.

Each of these spectral classes, except possibly for the Y class which is still being defined, is further subdivided into 10 subclasses designated by the numbers 0 through 9. A B0 star is the hottest type of B star; a B9 star is the coolest type of B star and is only slightly hotter than an A0 star. And just one more item of vocabulary: for historical reasons, astronomers call all the elements heavier than helium metals , even though most of them do not show metallic properties.

If you are getting annoyed at the peculiar jargon that astronomers use, just bear in mind that every field of human activity tends to develop its own specialized vocabulary. Just try reading a credit card or social media agreement form these days without training in law! It is these details that allowed Annie Cannon to identify the spectral types of stars as quickly as three per minute! As Figure 2 shows, in the hottest O stars those with temperatures over 28, K , only lines of ionized helium and highly ionized atoms of other elements are conspicuous.

Hydrogen lines are strongest in A stars with atmospheric temperatures of about 10, K. Ionized metals provide the most conspicuous lines in stars with temperatures from to K spectral type F. In the coolest M stars below K , absorption bands of titanium oxide and other molecules are very strong.

By the way, the spectral class assigned to the Sun is G2. The sequence of spectral classes is summarized in Table 1. This graph shows the strengths of absorption lines of different chemical species atoms, ions, molecules as we move from hot left to cool right stars.

The sequence of spectral types is also shown. Suppose you have a spectrum in which the hydrogen lines are about half as strong as those seen in an A star. Looking at the lines in our figure, you see that the star could be either a B star or a G star. But if the spectrum also contains helium lines, then it is a B star, whereas if it contains lines of ionized iron and other metals, it must be a G star.

If you look at Figure 3, you can see that you, too, could assign a spectral class to a star whose type was not already known. All you have to do is match the pattern of spectral lines to a standard star like the ones shown in the figure whose type has already been determined. This image compares the spectra of the different spectral classes. The spectral class assigned to each of these stellar spectra is listed at the left of the picture.

The strongest four lines seen at spectral type A1 one in the red, one in the blue-green, and two in the blue are Balmer lines of hydrogen. Note how these lines weaken at both higher and lower temperatures, as Figure 2 also indicates. The strong pair of closely spaced lines in the yellow in the cool stars is due to neutral sodium one of the neutral metals in Figure 2.

Both colors and spectral classes can be used to estimate the temperature of a star. Spectra are harder to measure because the light has to be bright enough to be spread out into all colors of the rainbow, and detectors must be sensitive enough to respond to individual wavelengths.

In order to measure colors, the detectors need only respond to the many wavelengths that pass simultaneously through the colored filters that have been chosen—that is, to all the blue light or all the yellow-green light.

Annie Jump Cannon was born in Delaware in In , she went to Wellesley College, one of the new breed of US colleges opening up to educate young women. Wellesley, only 5 years old at the time, had the second student physics lab in the country and provided excellent training in basic science. After college, Cannon spent a decade with her parents but was very dissatisfied, longing to do scientific work. Figure 4: Annie Jump Cannon — Cannon is well-known for her classifications of stellar spectra.

In the late s, the director of the Harvard Observatory, Edward C. Pickering, needed lots of help with his ambitious program of classifying stellar spectra. The basis for these studies was a monumental collection of nearly a million photographic spectra of stars, obtained from many years of observations made at Harvard College Observatory in Massachusetts as well as at its remote observing stations in South America and South Africa.

Pickering quickly discovered that educated young women could be hired as assistants for one-third or one-fourth the salary paid to men, and they would often put up with working conditions and repetitive tasks that men with the same education would not tolerate. These women became known as the Harvard Computers. We should emphasize that astronomers were not alone in reaching such conclusions about the relatively new idea of upper-class, educated women working outside the home: women were exploited and undervalued in many fields.

This is a legacy from which our society is just beginning to emerge. The basic system of a letter to denote spectral class is further refined by adding a number from 0 to 9 following it.

Each spectral class is thus broken down into ten subdivisions so that, for example, an F2 star is hotter than an F7 star. The basic characteristics of each spectral class are summarised in the following table. The four columns on the right of the table provide comparison of a star's mass, radius and luminosity power output with respect to the Sun and the main sequence lifespan for a star of that spectral class. These factors are discussed in more detail in later sections of the site.

One problem facing early attempts at classifying stellar spectra was the fact that two spectra could have the same lines present, indicating that the stars had the same effective temperature, but the lines in one star's spectrum were broader than in the other.

When the star's were plotted on an HR diagram it also became apparent that two stars could have the same effective temperature hence also colour and spectral class but vary enormously in luminosity and thus absolute magnitude. To account for this a second classification scheme of Luminosity Class was added to the original concept of Spectral Class.

A simplified version of the MK system of luminosity classes is shown in the table below. Skip to main content. Australia Telescope National Facility. Accessibility menu. Interface Adjust the interface to make it easier to use for different conditions. Interface Size.

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In general, however, the spectral type alone is not enough to allow us to estimate luminosity. A G2 star could be a main-sequence star with a luminosity of 1 L Sun , or it could be a giant with a luminosity of L Sun , or even a supergiant with a still higher luminosity. Remember, for example, that we can detect pressure differences in stars from the details of the spectrum.

This knowledge is very useful because giant stars are larger and have lower pressures than main-sequence stars, and supergiants are still larger than giants.

If we look in detail at the spectrum of a star, we can determine whether it is a main-sequence star, a giant, or a supergiant. Suppose, to start with the simplest example, that the spectrum, color, and other properties of a distant G2 star match those of the Sun exactly. It is then reasonable to conclude that this distant star is likely to be a main-sequence star just like the Sun and to have the same luminosity as the Sun.

But if there are subtle differences between the solar spectrum and the spectrum of the distant star, then the distant star may be a giant or even a supergiant. The most widely used system of star classification divides stars of a given spectral class into six categories called luminosity classes.

These luminosity classes are denoted by Roman numbers as follows:. The full spectral specification of a star includes its luminosity class. For example, a main-sequence star with spectral class F3 is written as F3 V. Figure 1 illustrates the approximate position of stars of various luminosity classes on the H—R diagram. The dashed portions of the lines represent regions with very few or no stars. Figure 1: Luminosity Classes. Stars of the same temperature or spectral class can fall into different luminosity classes on the Hertzsprung-Russell diagram.

By studying details of the spectrum for each star, astronomers can determine which luminosity class they fall in whether they are main-sequence stars, giant stars, or supergiant stars. As before, if we know how luminous the star really is and see how dim it looks, the difference allows us to calculate its distance. For historical reasons, astronomers sometimes call this method of distance determination spectroscopic parallax , even though the method has nothing to do with parallax.

The H—R diagram method allows astronomers to estimate distances to nearby stars, as well as some of the most distant stars in our Galaxy, but it is anchored by measurements of parallax.